Such electronic sandwich structures are used in numerous electronic components, in particular in components for power electronics. Silver sintered connections are used wherever high currents or high current densities, a very good heat transfer, i.e. high thermal flows, and a reliable mechanical load-bearing capacity have to be ensured. For this purpose, the parts to be joined that are to be sintered together are connected to one another with a material bond by a silver sintering layer that is as uniformly thin as possible (typically with a thickness of 10 to 50 μm) and is compacted to a greater or lesser degree. Apart from a uniform layer thickness, it is aimed to achieve a distribution that is as homogeneous as possible of the silver particles and other fillers in the sintered connecting layer. In particular, the so-called low-temperature connecting technique has become known for this. This is used in particular in the production of large-area bipolar semiconductors. In addition, this technique is also being used in IGBT module production. For the low-temperature connecting technique, silver powder and chemical additives at moderate temperatures of approximately 230° C. under high mechanical loads of about 20 to 30 MPa are used as a connecting material and sintering conditions are used for sintering together two parts to be joined. In this case, a porous connecting layer is created between a substrate and a semiconductor. This sintered connection is normally relatively strong and represents a homogeneous connection between the semiconductor and the substrate. Disadvantages for such a connecting method, especially with regard to mass production, are the high material costs, the incompatibility with today's soldering technologies, the quite extreme process parameters, the relatively long sintering process, the necessity to use precious metals and complex tools and machines.
In addition to this there is the fact that the parts to be joined that are to be sintered together also typically consist of dissimilar materials. This does also have the advantage that metals and metallized non- and semiconductor metals can be reliably connected. However, such dissimilar materials to be joined generally also have different coefficients of thermal expansion (CTE). This has the effect that after the joining, there are thermomechanical stresses in the material composite, which under some circumstances may lead to the electronic sandwich structure becoming damaged during use.
WO 2013/053420 A1 discloses a power semiconductor chip, which has on the upper side potential surfaces on which a metal molded body is fixed in an electrically and thermally well-conducting manner. Such a metal molded body is fastened onto a metallization layer of the semiconductor with the aid of a connecting layer by low-temperature sintering technology or else by way of diffusion soldering or adhesive bonding.
A method for providing a connection between metal molded bodies and a power semiconductor chip is described in WO 2013/053419 A1.
The thermomechanical mismatch of the parts to be joined must be sufficiently offset by the connecting layer. This means that the specified properties are retained over the fixed time period. It has therefore been attempted to form the sintered connecting layer as uniformly and thinly as possible, in order that virtually equally good properties are present at all points. There are application areas for silver sintering in which the parts to be joined have very different coefficients of thermal expansion, or at least one part to be joined is of a very fragile form. In these cases, the elasticity of the silver sintering layer is not sufficient, and the mismatch leads to shear stresses, which may ultimately end up destroying the integrity of the silver sintering layer or of a contact layer of one part to be joined.